The present invention relates to an improvement of precision pulse placement, in particular for precision pulse placement representing a pulse width modulation (PWM) or pulse position modulation (PPM) for precision analog signal generation using a waveform generator.
Pulse width modulation (PWM) may be used for analog signal generation. While the pulse rate has to be kept constant, signal processing calculates the ideal pulse width. The ideal pulse width depends upon the analog signal to be generated and may be found using natural sampling, click modulation, zero position coding (ZePoC) or uniform sampling.
Knowing the ideal pulse width it is usually quantized to the nearest multiple of a high frequency bit clock resulting in a realized pulse width, which is different from the ideal pulse width. As a consequence of this process a quantization error will arise. The quantization error depends upon the deviation of the ideal pulse width as calculated by signal processing from the realized pulse width. The quantization error will increase according to the deviation between ideal and realized pulse width. In prior art like US 2002/0180547 A1 tabs from a fine buffer delay chain are used to obtain fine timing resolutions.
The quantization error mentioned above can be noise-shaped. To effectively noise-shape the quantization error in a pre-processing algorithm the quantization error caused by the quantization process as described above needs to be well predictable. Fine timing by the use of tabs from a fine buffer delay chain like in US 2002/0180547 A1 does not fulfill this requirement because the delay of single buffers within the buffer delay chain may vary from unit to unit and may not be exactly known in advance. As a consequence noise-shaping in this case may not significantly improve the signal quality.